C#中[]的使用

c#中的方括号可用于数组，索引，属性，更重要的是可以用于外部Dll类库的引用。

C#实现.NET组件与COM组件的互操作

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[DllImport(“kernel32.dll”)]这叫引入kernel32.dll这个动态连接库。
这个动态连接库里面包含了很多WindowsAPI函数,如果你想使用这面的函数，就需要这么引入。举个例子：
[DllImport(“kernel32.dll”)]
private static extern void 函数名(参数，[参数]);

extern 作用：标识这个变量或者函数定义在其他文件 ，提示编译器遇到此变量的时，在其他模块里寻找，这里是在提供的动态库里找

函数名就是一个属于kernel32.dll里的一个函数。完了你就可以用那个函数了。
.NET组件中使用目前存在的COM组件
对于.NET来讲，使用COM组件就要简单一些。..NET提供了大量的类库来方便的实现同COM的相互操作，其中很重要的一个名称空间（nameSpace）就是：System.Runtime.InteropServices。通过这个名称空间的名字我们也可以从字面上看出，”互操作服务”。System.Runtime.InteropServices这个名称空间提供了一系列的类来对COM对象进行操作。
例子： 内存，硬盘的利用率

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;
namespace Windows.Help
{
public partial class SystemInfo : Form
{
public SystemInfo()
{
InitializeComponent();
}
[DllImport("kernel32")]
public static extern void GetWindowsDirectory(StringBuilder WinDir, int count);
[DllImport("kernel32")]
public static extern void GetSystemDirectory(StringBuilder SysDir, int count);
[DllImport("kernel32")]
public static extern void GetSystemInfo(ref CPU_INFO cpuinfo);
[DllImport("kernel32")]
public static extern void GlobalMemoryStatus(ref MEMORY_INFO meminfo);
[DllImport("kernel32")]
public static extern void GetSystemTime(ref SYSTEMTIME_INFO stinfo);
//定义CPU的信息结构
[StructLayout(LayoutKind.Sequential)]
public struct CPU_INFO
{
public uint dwOemId;
public uint dwPageSize;
public uint lpMinimumApplicationAddress;
public uint lpMaximumApplicationAddress;
public uint dwActiveProcessorMask;
public uint dwNumberOfProcessors;
public uint dwProcessorType;
public uint dwAllocationGranularity;
public uint dwProcessorLevel;
public uint dwProcessorRevision;
}
//定义内存的信息结构
[StructLayout(LayoutKind.Sequential)]
public struct MEMORY_INFO
{
public uint dwLength;
public uint dwMemoryLoad;
public uint dwTotalPhys;
public uint dwAvailPhys;
public uint dwTotalPageFile;
public uint dwAvailPageFile;
public uint dwTotalVirtual;
public uint dwAvailVirtual;
}
//定义系统时间的信息结构
[StructLayout(LayoutKind.Sequential)]
public struct SYSTEMTIME_INFO
{
public ushort wYear;
public ushort wMonth;
public ushort wDayOfWeek;
public ushort wDay;
public ushort wHour;
public ushort wMinute;
public ushort wSecond;
public ushort wMilliseconds;
}
private void button1_Click(object sender, EventArgs e)
{
//调用GetWindowsDirectory和GetSystemDirectory函数分别取得Windows路径和系统路径
const int nChars = 128;
StringBuilder Buff = new StringBuilder(nChars);
GetWindowsDirectory(Buff, nChars);
WindowsDirectory.Text = "Windows路径：" + Buff.ToString();
GetSystemDirectory(Buff, nChars);
SystemDirectory.Text = " 系统路径：" + Buff.ToString();
//调用GetSystemInfo函数获取CPU的相关信息
CPU_INFO CpuInfo;
CpuInfo = new CPU_INFO();
GetSystemInfo(ref CpuInfo);
NumberOfProcessors.Text = "本计算机中有" + CpuInfo.dwNumberOfProcessors.ToString() + "个CPU";
ProcessorType.Text = "CPU的类型为" + CpuInfo.dwProcessorType.ToString();
ProcessorLevel.Text = "CPU等级为" + CpuInfo.dwProcessorLevel.ToString();
OemId.Text = "CPU的OEM ID为" + CpuInfo.dwOemId.ToString();
PageSize.Text = "CPU中的页面大小为" + CpuInfo.dwPageSize.ToString();
//调用GlobalMemoryStatus函数获取内存的相关信息
MEMORY_INFO MemInfo;
MemInfo = new MEMORY_INFO();
GlobalMemoryStatus(ref MemInfo);
MemoryLoad.Text = MemInfo.dwMemoryLoad.ToString() + "%的内存正在使用";
TotalPhys.Text = "物理内存共有" + MemInfo.dwTotalPhys.ToString() + "字节";
AvailPhys.Text = "可使用的物理内存有" + MemInfo.dwAvailPhys.ToString() + "字节";
TotalPageFile.Text = "交换文件总大小为" + MemInfo.dwTotalPageFile.ToString() + "字节";
AvailPageFile.Text = "尚可交换文件大小为" + MemInfo.dwAvailPageFile.ToString() + "字节";
TotalVirtual.Text = "总虚拟内存有" + MemInfo.dwTotalVirtual.ToString() + "字节";
AvailVirtual.Text = "未用虚拟内存有" + MemInfo.dwAvailVirtual.ToString() + "字节";
//调用GetSystemTime函数获取系统时间信息
SYSTEMTIME_INFO StInfo;
StInfo = new SYSTEMTIME_INFO();
GetSystemTime(ref StInfo);
Date.Text = StInfo.wYear.ToString() + "年" + StInfo.wMonth.ToString() + "月" + StInfo.wDay.ToString() + "日";
Time.Text = (StInfo.wHour + 8).ToString() + "点" + StInfo.wMinute.ToString() + "分" + StInfo.wSecond.ToString() + "秒";
}
private void button2_Click(object sender, EventArgs e)
{
this.Close();
}
}
}